1. Technical Field
The present invention relates to a light source device, an illuminating device, a monitoring apparatus, and a projector, and more particularly, to a technology of a light source device using a wavelength converting element.
2. Related Art
As a light source device for a monitoring apparatus or a projector, a technology using a laser light source supplying a laser light has been suggested. In comparison with a UHP lamp used in the past as the light source device for a monitoring apparatus or a projector, the laser light source has advantages that color reproducibility is high, instantaneous lighting is possible, and lifetime is long. As the laser light source, a light source directly supplying a basic wavelength light from a light-emitting section and a light source converting and supplying the basic wavelength light in wavelength are known. For example, a second-harmonic generation (SHG) element is used as a wavelength converting element converting the wavelength of the basic wavelength light. By employing the wavelength converting element, it is possible to supply a laser light of a desired wavelength by the use of a general-purpose laser light source which is easily available. It is also possible to supply a laser light with sufficient intensity. It is known that the wavelength conversion efficiency of an incident light incident on the SHG element is about in the range of 30% to 40%. In a configuration allowing the basic wavelength light to be simply incident on the SHG element, the intensity of the harmonic light converted in wavelength by the SHG element is much smaller than the intensity of the basic wavelength light. A technology of supplying a laser light converted in wavelength with high efficiency is disclosed, for example, in JP-A-59-128525. In the technology disclosed in JP-A-59-128525, a basic wavelength light is separated from a light passing through the SHG element and is allowed to be incident on the SHG element again.
In the configuration disclosed in JP-A-59-128525, a complex and great structure is necessary to synthesize the light converted in wavelength by the SHG element and the light converted in wavelength by allowing the basic wavelength light once passing through the SHG element to be incident on the SHG element again. The optical loss increases by allowing lights to be incident on many optical elements. In other configurations suggested in the past such as a configuration in which lights are separated by the use of a switch structure disposed inside a resonator (JP-A-7-86668) and a configuration in which lights are separated by the use of a mirror disposed inside a resonator (U.S. Pat. No. 5,761,227), the same problems as JP-A-59-128525 such as the complication in configuration, the increase in size, and the optical loss are caused. These known configurations have a problem in that it is difficult to obtain high wavelength conversion efficiency with a simple and small configuration.